The present invention relates to an analog/digital mixed integrated circuit by which an analog circuit and a digital circuit are integrated within a single semiconductor chip.
In recent years, in addition to cellular-phone equipment and PDA (Personal Digital Assistants), many electronics devices, including entertainment equipment such as radio receiver, digital camera, and game machine, etc.; home electronics such as air conditioner and refrigerator; vending machine; manufacturing equipment in a factory; measuring apparatus; in-vehicle equipment such as car navigation system, etc.; and business equipment, etc., have means of communication, and have been utilized as network terminals.
Under such a networked environment, wireless communications make communication xe2x80x9cwhenever, wherever, and to whomeverxe2x80x9d possible. As means of wireless communications, there are Bluetooth for short-distance wireless data communication technology, and wireless LAN using an addition to cellular-phone system or a 5 GHz band, in addition to cellular-phone system or PDA.
Regarding such communication terminals, xe2x80x9cbeing ultra-portablexe2x80x9d is a prerequisite as a matter of course. Thus, miniaturization, light weight, and low-power consumption are strongly required. Generally speaking, wireless communication terminals tend to have multifunctions and high performance. Even so, regarding the entirety of equipment, miniaturization, light weight, and low-power consumption are required. Therefore, for the wireless communication functions built-in equipment, further miniaturization, light weight, thinness, and low-power consumption are required.
In light of such a background, the development of multifunctions, high integration, and high density for semiconductor integrated circuits has rapidly progressed. Trials in which radio frequency circuits including passive component parts such as condensers, etc., are made into a single chip or a single modularization have been performed. Recently, there have also been developments in which the past independence of analog LSI and digital LSI has given way to integration in the form of an analog/digital mixed LSI.
For example, trials where radio frequency circuit (analog circuit) used to transmit and receive analog signals, and PLL (Phase Locked Loop) synthesizer circuit (digital circuit) or baseband signal processing circuit (digital circuit) used so as to perform digital signal processing of the signals to transmit and received signals are made into a single chip or a single modulation have been actively made.
The analog circuit and digital circuit in an analog/digital mixed integrated circuit are arranged adjacently each other, compared with the structure where analog and digital circuits are arranged on separate chips. Thus, in many cases, significant noise from the digital circuit tends to enter the supersensitive analog circuit. In such cases, the characteristics of the analog signals become extremely deteriorated. Therefore, the way in which such coupling noise arising from analog and digital circuits is reduced is very important.
In particular, for the digital circuit, a clock signal as a control standard is supplied. In such a case, when an analog circuit (for example, a high frequency circuit) is arranged near an digital circuit, high frequency components of the clock signal jump into the analog circuit as digital noise, which largely deteriorates the characteristics of the analog signals transmitted and received wirelessly. For instance, when audio signals are transmitted and received, the receiving sensitivity declines, and the sound quality becomes remarkably deteriorated, which causes extreme difficulty in terms of hearing.
Therefore, for example, a front-end part of a high frequency circuit, etc. is composed of an analog circuit, and the baseband signal processing circuit is composed of a digital circuit, etc. So, either the analog circuit or the digital circuit is organized according to functional unit. This separates the analog circuit area from the digital circuit area on the chip layout.
However, as shown in FIG. 1, depending on uses of an analog/digital mixed integrated circuit, there exist some circuits switching through the clock signal even within the analog circuit area (in this specification, an operated circuit based on the clock signal is called a switching circuit).
Meanwhile, a clock generator circuit that generates a clock signal is normally arranged in the digital circuit area. In such case, the length of a clock line that is wired from the clock generator circuit arranged in the digital circuit area to a switching circuit arranged in the analog circuit area becomes long. However, the intervals between wirings or between parts become very narrow for high-integration and high-density-ized analog/digital mixed integrated circuits. Thus, the influence of the clock signal flowing through the long clock line upon the surroundings becomes large.
In particular, when a high frequency amplification circuit, etc. corresponding to the transmission and reception section of the high frequency signals exits near the clock line, the digital noise by the clock signal jumps into the high frequency amplification circuit, which causes the characteristics of the analog signals to become remarkably deteriorated. Energies of the clock signal become larger as the frequency becomes higher. Thus, the problem stated above becomes more remarkable as the frequency of the clock signal becomes higher.
The purpose of the present invention is to suppress the inconvenience where the digital noise by the clock signal flowing through the clock line is received by the analog circuit, and the quality of the analog signals becomes deteriorated.
An analog/digital mixed integrated circuit of the present invention mixes analog circuits and digital circuits within the same semiconductor chip, an analog circuit area and a digital circuit area are held within the semiconductor chip, a clock generator circuit that generates a clock signal is arranged within the digital circuit area, and a switching circuit that performs switching operation by the clock signal and performs analog signal processing is arranged within the digital circuit area.
Here, the switching circuit is preferably arranged near the clock generator circuit.
In another aspect of the present invention, an analog/digital mixed integrated circuit mixes analog circuits and digital circuits within the same semiconductor chip, the semiconductor chip includes a first switching circuit that operates based on a clock signal with a first frequency and performs analog signal processing, a second switching circuit that operates based on a clock signal with a second frequency higher than the first frequency and performs analog signal processing, and a clock generator circuit that generates a clock signal with the first and second frequency, and an analog circuit area and a digital circuit area are held within the semiconductor chip, the first switching circuit is arranged within the analog circuit area, and the second switching circuit and the clock generator circuit are arranged within the digital circuit area.
Here, the second switching circuit is preferably arranged near the clock generator circuit.
According to this present invention, shortening of the wiring length of the clock line that is routed from the clock generator circuit arranged within the digital circuit area of the semiconductor chip to the switching circuit that operates based on the clock signal is possible. Furthermore, the distance between the clock line and the analog circuits within the analog circuit area can be as great as possible. The distance between the switching circuit itself and the analog circuits within the analog circuit area can also be as great as possible.